Through the spread of information communication devices such as radio terminals, an extension of the frequency band used in the communication is accelerated from several hundreds MHz for the mobile phone, or the like to the several GHz band for the radio LAN, or the like. In the existing circumstance, terminals that are adaptable for various communication systems respectively are used independently. But the radio terminal that can conform to various communication systems alone is desired in the future.
Meanwhile, with the progress of a miniaturization of the radio terminal, a size reduction of passive parts such as a filter built in an enclosure of the terminal is desired. In the filter utilizing the LC electric resonance, or the like that is often used particularly in the radio communication in recent years, a resonator size depends on an electric length. As a result, such a problem lies that a miniaturization of the filter is difficult, and thus it is tried to grope for the new principle of signal selection.
Among various approaches, the development of the GHz band element using the magnetic material is stimulated. An attempt to use the magnetic material in the passive element aiming at the high frequency band from several hundreds MHz to several GHz band or more ranges up to the filter for the high-frequency transmission line. As its advantage, it may be listed that such filter using the magnetic metal material such as Fe, or the like is excellent in the temperature characteristic and the saturation magnetization and is suitable for the integration to IC. Recently it was reported that a wavelength shortening effect can be increased by introducing the magnetic metal, and thus the expectation is running high for the miniaturization of the element rises.
As the filter using the magnetic material, there is Non-Patent Literature 1, for example. In this Non-Patent Literature 1, the Fe/GaAs substrate hybrid microstrip line in which the microstrip line made of the ferromagnetic film containing Fe is formed on the GaAs substrate is constructed, and thus the 10 GHz band band-stop filter is realized by utilizing the ferromagnetic resonance phenomenon. A ferromagnetic resonance frequency f of this band-stop filter is given by Eq. (1). Where γ is a gyromagnetic constant (1.105×105 g [A−1m·s−1], g:Land′e's factor), Ha is an anisotropic magnetic field (A/m), Is is a saturation magnetic field (T), and H is a DC bias magnetic field.
The anisotropic magnetic field Ha is given by Eq. (2) from the crystal magnetic anisotropy constant K1 ˜48 kl/m3 and the saturation magnetization Is ˜2.15 T of the single crystal Fe film. Since g˜2 in the transition metal Fe, the ferromagnetic resonance frequency becomes about 9.85 GHz when the external DC bias magnetic field H is zero.
The ferromagnetic resonance frequency can be tuned by changing an intensity of the DC bias magnetic field H, and thus the tunable filter can be realized.
Also, the value of the ferromagnetic resonance frequency depends on not only the intensity of the DC bias magnetic field H but also the vector thereof. Eq. (1) expresses the case where the high-frequency magnetic field generated by the strip line current intersects orthogonally with the magnetic moment generated by the DC bias magnetic field. The ferromagnetic resonance does not occur when the high-frequency magnetic field and the magnetic moment are directed in the same direction. The vector of the DC bias magnetic field H must also be regarded.
Non-Patent Literature 1: E. Schloemann et al.,: J. Appl. Phys., 63,3140 (1998)